The objective of this proposal is to optimize methods of male germ cell transfection and transplantation for use in producing transgenic goats. The milk of transgenic goats is a safe, abundant and cost effective production source for recombinant human biopharmaceuticals. GTC Biotherapeutics (formerly Genzyme Transgenics Corp.) has nearly two dozen commercial transgenic programs in development. However, even state-of-the-art methods for generating transgenic founder (first generation) goats remain relatively inefficient and expensive. Methods have been developed in rodents for transplanting genetically modified male germ cells into recipient males and mating these animals to produce transgenic offspring. A similar system has shown some early success in pigs, and preliminary studies suggest that it may be feasible in goats. Now we propose to: 1) optimize methods of enriching donor germ cell preparations; 2) optimize methods of transfecting transgene constructs into these donor cells in vitro; and 3) confirm that homologous germ cell transplantation in goats results in the production of morphologically normal, motile sperm carrying the transgene. If this approach is successful, it will increase the efficiency and reduce the cost of generating founder animals, which is a critical early step in the transgenic production process. [unreadable] [unreadable]